Polypropylene and polypropylene copolymers may be formed in a polymerization reactor in the presence of an appropriate catalyst. Propylene monomer is introduced into the reactor, alone or in combination with one or more other monomers, such as ethylene, to produce the polypropylene homopolymer or copolymer fluff or granules. The propylene polymer is withdrawn from the reactor and may be subjected to appropriate processing steps and then extruded as a thermoplastic mass through an extruder and die mechanism to produce the propylene polymer as a raw material in particulate form, usually as pellets. The propylene polymer pellets are ultimately heated and processed in the formation of the desired end products. Examples of such end products include fibers, webs (both woven and nonwoven), films, pipe, containers, and foamed articles. Other examples of such products made from propylene polymers include component parts of durable goods articles such as automotive interior and exterior components, and household appliance interior and exterior components.
One form of reactor suitable for polypropylene homopolymer and copolymer production is a bulk loop reactor. A bulk loop reactor may be formed from one or more interconnected loops having a continuous bore. The catalyst is distributed within the continuous bore by circulating liquid propylene monomer. In this way, propylene polymer polymerization occurs within the continuous bore. Two or more bulk loop reactors may be connected, such as for example in series. In this way, the polymerization conditions in each reactor may be the same or different to achieve desired polymer properties. Examples of polymerization conditions that may be varied include temperature, pressure, monomer content, co-monomer content, catalyst, co-catalyst and hydrogen concentration.
Polymer particles exiting the bulk loop reactor may be subjected to processing steps as described above or they may be introduced into one or more polymerization reactors, such as for example one or more gas phase reactors, for further polymerization with other monomers, such as ethylene, to alter the physical and chemical properties of the propylene polymer resins. Additionally, the physical and chemical properties of the propylene polymer resin may be tailored by the selection of one or more catalyst systems.
Because bulk loop reactors can produce propylene polymers on a substantially continuous basis, and at high out-puts over an extended period of time, such as for example, from between 1 to at least 50 tons of propylene polymer per hour for between 5 days to up to 2 years and beyond, bulk loop reactors offer several advantages over other types of polypropylene reactors, such as stirred pot, stirred bed, and other non-substantially continuous reactors. However, while there may be more than one catalyst system useful for producing polypropylene, in some instances the presence of small quantities of one catalyst system or small quantities of one or more of the components thereof may interfere with or hinder the performance of another catalyst system. As such, while there may be several catalysts systems useful for the production of polypropylene, not all such catalysts systems are compatible in combination with each other. Furthermore, while the design and or physical environment within a bulk loop reactor and associated equipment may be suitable for production of polypropylenes using one catalyst system, these conditions and/or design may be less than suitable or less than desirable for production of polypropylenes using another catalyst system. Therefore, in order to take advantage of the benefits offered by bulk loop reactors, there exist a need to avoid such problems when using different catalyst systems in a common bulk loop reactor to produce propylene polymers.